1. Field of the Invention
This invention resides in the field of laboratory apparatus for performing electrophoresis in a horizontally oriented slab gel submerged in a liquid buffer solution.
2. Description of the Prior Art
The technology of electrophoresis to separate proteins, nucleic acids, or other charged species in biological mixtures of various sorts has now developed into systems and methods that employ a wide variety of geometries and techniques. One of the most common forms of electrophoresis and one that is among the simplest to use, particularly for the analysis of nucleic acids, is electrophoresis in a horizontally oriented slab gel which is submerged in a liquid buffer solution. This is commonly known as xe2x80x9csubmerged gel electrophoresisxe2x80x9d or xe2x80x9csubmarine electrophoresis.xe2x80x9d Horizontal systems offer the advantage of a convenient arrangement of anode and cathode buffer reservoirs along two opposing edges of the gel and an ease of placing the gel in the electrophoresis cell and removing the gel once the separation has been completed. Submarine systems arose from the discovery that a proper and controllable current could be maintained between opposing edges of the gel even when a single buffer solution occupies the reservoirs along both edges and continues in a thin layer along the top surface of the gel. Among the many advantages of submarine systems are that the upper surface of the gel can be left exposed, which facilitates its removal or allows the user to stain the gel without removing it. Agarose gels are commonly used in these systems, although other conventional electrophoresis gels can be used as well.
Submarine electrophoresis cells are commercially available from many suppliers, each having its own unique characteristics. A typical construction includes a tank and lid with appropriate electrical connections to impose a voltage within the tank, the tank molded to include a pair of elongated wells for the electrodes, the wells separated by a raised platform which supports the gel. The electrodes are supported in each well are at a height below the level of the platform. A problem that arises with cells of this type is that when the tanks are filled with enough buffer solution to submerge the gel, the gel has a tendency to move or float during sample loading and during electrophoresis, and this movement or floating can affect the results. If uncontrolled, the drift can be detrimental to reproducibility and can result in the loss of a run.
The gels used in submarine electrophoresis cells can either be formed in the cell itself, in which they are cast by the user in trays, or they can be precast by a supplier in trays which are then placed inside the cell. Precast gels offer numerous advantages, including the elimination of operator error or variation in the casting of the gel as well as a considerable reduction in time and labor involved in setting up and performing an electrophoretic separation. Unfortunately, both gels that are cast by the user in the cell and gels that are precast are susceptible to the movement and floating.
The factors noted above and others arising in the design and use of submarine electrophoresis cells are addressed by the present invention, which resides in a precast electrophoresis gel and the tray in which the gel is cast, the tray containing features that prevent the lateral drift of the gel during electrophoresis and stabilize both the gel and tray during sample loading and electrophoresis. Like trays of the prior art, the tray of the present invention has a flat base and raised walls on two opposing sides, leaving the remaining two sides open for electrical contact with the anode and cathode through the intervening buffer solution. Unlike the prior art, however, the tray contains one or more tabs extending outward from the exterior surface(s) of the raised wall(s), the tabs mating with grooves in the interior walls of the tank. With the tabs inserted in the grooves, the lateral drift of the tray is prevented from occurring. The tabs are readily designed to mate with grooves that are present in the tank for other purposes, which adds to the versatility of the design. Further versatility is achieved by tabs that are readily removable, thereby rendering the tray usable in cell tanks that do not contain grooves.
This invention also resides in a series of protrusions or posts extending upward from the base of the tray, designed such that when a gel is cast in the tray the posts hold the gel in place and prevent it from moving within the tray. In a still further aspect, the invention resides in the inclusion of fluorescent indicia printed on the base of the tray to assist in the identification or differentiation of individual samples, or to indicate the distance of migration of components in individual samples, or both. The indicia are applied by a printing process that includes hot foil stamping. These and other features and aspects of the invention will be better understood by the description that follows.